This invention relates to measuring and testing systems, and more particularly, it relates to the measurement and sampling downhole in an oil well of the gas content in formation fluids.
It has been a common practice to evaluate the productivity of an oil well by using downhole wireline instruments. These instruments have varied from most complex to the very elementary types. Some formation testing instruments are capable of measuring many downhole parameters, e.g., temperature, pressure, flow rates, conductivity, etc., and sending the resulting information to the surface equipment for recording and evaluation. If this data were favorable of petroleum prospects, a sampling tool was then used to take a sample of the formation fluid.
The sample taking tools are simply a body with valving to allow an internal chamber to be filled with formation fluid. The tool then was raised to the surface and the formation fluid subjected to analysis for petroleum values.
The problem with these prior formation testing and sampling tools concerns the determination of taking a sample only when the formation fluid has petroleum values and not solely water. The particularly measured qualities in the petroleum containing formation fluid are the gas and oil contents.
The gas content in the formation fluid from a downhole producing formation is very vital information in making a commercial evaluation of petroleum production. It is especially important that this information be obtained quickly, and in a manner compatible with computer processing techniques so that the measurements are made in real time.
A formation pressure test can be made in a wellbore by opening a small chamber to be filled by formation fluid. Pressure sensors can measure the formation fluid pressure in the wellbore and also in the chamber. However, these pressure measurements provide no definitive information of the formation fluid character since high pressures can exist in gas, oil and water producing formations.
An expansion-type valve can be placed at the inlet to the chamber so that formation fluids containing gas at elevated pressures will produce a temperature reduction in their flow through the valve and into the reduced pressure environment of the chamber. Naturally, formation fluid without a gas content produces no significant temperature change in flowing through the expansion-type valve.
The present invention uses in combination, the above discussed pressure and temperature measurements and functions of these variables, as an indicator of the gas content of formation fluids so that an immediate determination can be made to take a sample of hydrocarbon bearing formation fluids.